1. Field of the Invention
This invention relates to magnetic heads or transducers and more particularly to such heads which provide a tunnel erasing action by means of erasing cores having gaps therein on an active face of the head on opposite sides of a central read/write core having a read/write gap in said active face.
2. Description of the Prior Art
Childers et al. U.S. Pat. No. 3,846,840, issued Nov. 5, 1974, discloses (see FIG. 1 in particular of this patent) a magnetic head which accomplishes tunnel erase by means of a pair of erase gaps disposed in cores on opposite sides of a central core in which a read/write gap is provided. Although the magnetic head of this patent is useful particularly for low density recording; when it is used for very high density recording, noise sources superimposed on the electrically fluctuating signal during either the record or playback processes significantly reduce the ability of the system in which the head is disposed to recover the recorded data. Two noise sources, applicable to the tunnel erase configurations and commonly used in connection with flexible disks, such as that disclosed in Flores et al. U.S. Pat. No. 3,668,658 issued June 6, 1975, are relevant to the invention hereof and are as follows:
(1) Imperfect guard band generation. If the magnetic flux in the erase gaps, which functions to tunnel erase on side guard bands and which is generated by the current in an erase coil, is not sufficient to saturate the magnetic medium, such as a magnetic disk with which the head is used, old data (previously recorded magnetic transitions) may not be completely erased. In addition, time varying magnetic flux from external sources, such as from the associated write magnetic circuit, superimposed on the magnetic erase flux can record weak magnetic transitions in the guard bands. In this case, if head-to-data track misregistration occurs during playback, the read/write gap is influenced by both the intended signal and also by noise from the old data and/or weak guard band magnetic transitions.
(2) Tunnel erase bias. With the head configuration of U.S. Pat. No. 3,846,840, a fraction of the magnetic flux in the tunnel erase gaps generated by current flowing through the erase coil also passes through the read/write gap. Assuming that the erasing action occurs at the same time as writing, as is quite often the case, this flux produced by the tunnel erase coil adds algebraically to the flux generated by the read/write coil and distorts the recording signal by upsetting the carefully balanced flux reversals of the recording signal.